The present invention pertains to an image projection system, and in particular to optical path components for an image projection system.
Projection systems have been used for years to project motion pictures and still photographs onto screens for viewing. More recently, presentations using multimedia projection systems have become popular for purposes such as sales demonstrations, business meetings, and classroom sessions. In a common mode of operation, multimedia projection systems receive analog video signals from a personal computer (PC). The video signals represent still, partial-, or full-motion display images of the type rendered by the PC. The analog video signals are converted into digital video signals to control a digitally-driven light valve, such as a reflective micro-mirror-type light valve or a transmissive liquid crystal light valve (LCD), which form display images.
A popular type of multimedia projection system is a projector that incorporates a light source and optical path components upstream and downstream of the light valve to project the display images onto a display screen. Examples such projectors include those sold under the trademark LITEPRO(copyright) by In Focus Systems, Inc. of Wilsonville, Oreg., the assignee of the present application.
Significant effort has been invested into developing lightweight, compact projectors, in order to increase the convenience of use. Decreased weight is particularly important for a multimedia projector designed for the mobile presentation market, wherein a presenter typically carries the projector on airplanes, through airport terminals, hotels, etc., and into presentation rooms for delivery of presentations. Thus, lightness of weight and compactness are two of the most noticeable and desirable attributes of portable multimedia projectors.
Efforts to decrease weight and increase compactness have been limited in part by the numerous mirrors and objective lenses in conventional projection optical systems. Such mirrors and lenses add significant bulk and weight to a projector. Furthermore, bulky frames are required for precisely positioning these optical elements along the projector optical path. Dispersion of these components in the projector may also cause heat generation in numerous dispersed areas of the projector, requiring a complex cooling system that adds additional weight and bulk to the projector.
Moreover, such mirrors, lenses and frames are expensive, especially when they require custom grinding. These components are also subject to damage and misalignment if the projector is inadvertently dropped or otherwise mishandled.
Thus, in light of these disadvantages, it is a principle object of the present invention to provide a light-weight projector optical system.
It is another object of the present invention to provide a compact projector optical system.
It is a further object of the present invention to provide an inexpensive projector optical system.
It is a further object of the present invention to provide a rugged projector optical system that is relatively invulnerable to mechanical damage.
In accordance with a preferred embodiment of the present invention an image projector is provided with a light source, a nonimaging device defined by the edge ray method positioned downstream of the light source, light valve positioned downstream of the nonimaging device, and a front lens system positioned downstream of the light valve. The light from the light source is projectable through the nonimaging device onto the light valve.
Such application of the nonimaging device permits a light-weight, tough and versatile light pipe to be utilized in the projector optical system upstream of the light valve, eliminating the need for numerous of the lenses and/or mirrors present in conventional image projectors.